1. Field of the Invention
The present invention relates to a clock spring connector applied to a steering device or the like of an automobile, wherein an electrical connection between a fixed member and a movable member is performed by use of a flexible cable.
2. Related Background Art
In a clock spring connector, a fixed member is connected through a flexible cable to a movable member so mounted as to be rotatable relative to this fixed member. The clock spring connector is employed as an electrical connecting means between the fixed member and the movable member having a finite number of revolutions as in the case of a steering device of an automobile.
In this type of clock spring connector, the flexible cable is high in terms of percentage of occupying the total costs. Proposed in the specification of U.S. Pat. No. 3,763,455 is a clock spring connector constructed to reduce the costs by decreasing a length of a flexible cable needed.
FIG. 26 is a plan view schematically illustrating a construction of the clock spring connector disclosed in the aforementioned patent specification. As shown in the same figure, a movable member 101 is so mounted as to be rotatable relative to a cylindrical fixed member 100. Flexible cables 103, 104 are housed in an ring-like air space 102 defined by the fixed member 100 and the movable member 101. These flexible cables 103, 104 are led to the outside of the air space 102 in such a state that the cables are fixed respectively to the fixed member 100 and the movable member 101. The flexible cables are accommodated in the air space 102 in a state where the cables are wound on an outer cylindrical unit of the fixed body 100 and on an inner cylindrical unit of the movable 101 in winding directions reverse to each other. A U-shaped turned-back portion is formed in the position where the winding direction is turned back. Further, groups of a plurality of rollers 105, 106 are disposed in the peripheral direction in the air space 102. The turned-back portion of the flexible cable 103 is looped with one group of the rollers 105, while the turned-back portion of the flexible cable 104 is looped with the other group of the rollers 106.
In the thus constructed clock spring connector, when, e.g., the movable member 101 is rotated clockwise in FIG. 26, the turned-back portions of the flexible cables 103, 104 also move in the peripheral direction of the air space 102. The flexible cables 103, 104 are rewound on the outer cylindrical unit of the fixed member 100 in a denser winding state. In reverse to this, when the movable member 101 is rotated counterclockwise in FIG. 26, the turned-back portions of the flexible cables 103, 104 also move in the same direction. The flexible cables 103, 104 are tightly wound on the inner cylindrical unit of the movable member 101 more densely. Note that during such a tight-wind or rewind operation, the respective rollers 105, 106 undergo the force given from the turned-back portions of the flexible cables 103, 104 and thereby move in the same direction.
According to the clock spring connector in the conventional example described above, the winding directions of the flexible cables are reversed with respect to the inner and outer cylindrical units. Hence, the lengths of the flexible cables required can be remarkably decreased as well as reducing the costs as compared with such a clock spring connector that the flexible cables are wound (in an eddy state) on the inner and outer cylindrical units in the same direction. Besides, the plurality of rollers are disposed between the inner cylindrical unit wound with the flexible cable and the outer cylindrical unit wound with the flexible cable. The flexible cables can be thereby regulated in the radial direction over the entire periphery of the ring-like air space. The tight-wind or rewind operation can be performed smoothly.
However, a dimension (indicated by the symbol L in FIG. 26) between the flexible cable wound on the inner cylindrical unit and the flexible cable wound on the outer cylindrical unit fluctuates depending on the winding states of the flexible cables. The dimension L becomes maximum when all the flexible cables are rewound on the outer cylindrical unit having a larger diameter. Whereas if all the flexible cables are wound tightly on the inner cylindrical unit having a smaller diameter, the dimension L becomes minimum. For this reason, even when the plurality of rollers are closely disposed in the air space on the assumption that the dimension L is minimum, and if the flexible cable is rewound densely on the outer cylindrical unit to increase the dimension L, backlashes are produced between the respective rollers and the flexible cables. On the other hand, a dimension (indicated by the symbol M in FIG. 26) in the peripheral direction of the air space defined by the flexible cable wound on the inner cylindrical unit and by the flexible cable wound on the outer cylindrical unit also fluctuates depending on the winding states of the flexible cables. When the all the flexible cables are rewound on the outer cylindrical unit having the larger diameter, the dimension M becomes minimum. Whereas if all the flexible cables are wound tightly on the inner cylindrical unit having the smaller diameter, the dimension M becomes maximum. For this reason, even when the rollers are closely disposed in the air space on the assumption that the dimension M is minimum, and if the flexible cables are wound tightly on the inner cylindrical unit to increase the dimension M, the backlashes are produced between the adjacent rollers. Hence, there arises such a problem that the rollers impinge on each other to cause strange noises due to those backlashes.
Further, when rotating the movable member in a state where the backlashes, as described above, exist between the respective rollers--especially when rotating the movable member in the rewinding direction, the flexible cable wound on the inner cylindrical unit swells towards the outer cylindrical unit on the way to the turned-back portion in such a place that a gap in the peripheral direction between the adjacent rollers is widened. The flexible cable then sinks in this gap. A problem is also caused, wherein this swelled part is buckled due to a further rotation of the movable member, resulting in a damage to the flexible cable.
In addition, although the force to cause the rotation in the same direction acts on all the rollers because of the contact with the flexible cable, the respective rollers rotate in the directions opposite to each other in such a place that the adjacent rollers are contact each other. Consequently, there is caused a problem in which the rotations of the rollers are offset, and a motion of the flexible cable is unsmooth.
Furthermore, it is required that a clearance for smoothing the movement of the flexible cable 103 be provided between the upper crosswise end of the flexible cable 103 and the top surface of the air space 102. However, a curvature of a turned-back portion 103a of the flexible cable 103 is remarkably smaller than others, and hence the turned-back portion 103a somewhat swells crosswise. This swollen part rubs against the top and bottom surfaces of the air space 102 during its movement. This causes a problem in which the flexible cable 103 can not be led out smoothly through the turned-back portion 103a.